Soil water repellency in the Brazilian neotropical savanna: first detection, seasonal effect, and influence on infiltrability.

Soil water repellency (SWR) has been detected worldwide in various biomes and climates. However, this phenomenon has not been shown yet in the Brazilian neotropical savanna. The present study addressed the following questions: (a) Does SWR occur in the Brazilian neotropical savanna? If so, (b) does it exhibit seasonality? (c) Does it influence infiltration? To do that, we selected two similar study areas covered by similar soils (oxisol) and vegetation (netropical savanna). We performed water repellency and infiltration tests in both areas during the transition from dry to wet season. Our results indicate that SWR occurs in soils of the Brazilian neotropical savanna only during the dry season and influence water infiltration in the dry season. The likely cause of SWR might be related to the chemical composition of soil organic matter since neotropical savanna plants produce hydrophobic substances as a survival strategy, especially during the dry season.

Topsoil physical properties under a riparian forest in Central Brazil: infiltration and penetration resistance / Propriedades físicas da camada superficial do solo em florestas ripária no Brasil central: resistência à infiltração e penetração

Plant composition, diversity and structure of riparian forests of Central Brazil are well known. However, little is known about soil physical properties under these forests. This knowledge is important as a baseline for biodiversity restoration and ecosystem services that occur in riparian zones. In order to bridge this gap, here we assessed the infiltration capacity and soil penetration resistance in a plinthic soil under gallery forest in Planaltina, Distrito Federal, Brazil. We measured infiltration capacity (Mini-Disk infiltrometer) and soil penetration resistance (Stof penetrometer) following linear transects. The plinthic soil had high infiltration capacity and low penetration resistance. Our infiltration estimate is in the middle range when compared to other permeability studies in tropical forests. Like their counterparts, high biological activity along with the lack of disturbance are the likely explanations for such high topsoil permeability to water.

As florestas de galeria são bem descritas em termos de composição, diversidade e estrutura da vegetação. No entanto, pouco se sabe sobre as propriedades físicas do solo sob essas florestas que são importantes para a restauração de zonas ripárias. A fim de preencher essa lacuna, no presente trabalho, avaliou-se a capacidade de infiltração e a resistência do solo à penetração em um solo plíntico sob floresta ripária em Planaltina, Distrito Federal, Brasil. Mediu-se a capacidade de infiltração (infiltrômetro de Mini-Disk) e a resistência à penetração no solo (penetrômetro de Stolf) seguindo transectos lineares. O solo plíntico apresentou alta capacidade de infiltração e baixa resistência à penetração. Nossa estimativa de infiltração está na faixa intermediária em comparação com outros estudos de permeabilidade em florestas tropicais. Mesmo assim, a mediana da capacidade de infiltração foi superior à intensidade de chuva de alto período de retorno o que descarta a possibilidade de escoamento superficial Hortoniano. Como em outras florestas tropicais, a alta atividade biológica junto com a ausência de perturbação do solo são as razões prováveis para essa alta permeabilidade do solo à água.

Stemflow generation as influenced by sugarcane canopy development.

Rainfall is generally partitioned into throughfall, stemflow, and interception in ecosystems. Stemflow variability can affect the hydrology, ecology, and soil chemistry patterns. However, the influence of canopy structure and rainfall characteristics on stemflow production in sugarcane plantations which are important for renewable energy production remain poorly understood. By using funnels attached to the sugarcane stems, the present study determined the stemflow amount during the period of sugarcane growth and its relationship with plant development. Approximately, 14% of gross rainfall reached the soil as stemflow, and the funneling ratios was 60. In general, it was observed a positive relationship between stemflow rates with both leaf area index and plant height. This was attributed to an increasing number of acute branching angles of the sugarcane leaves as well as high stem tillering and density. However, at the end of growth cycle, stemflow rate was lower than in previous periods which can be attributed to changes in sugarcane canopy such as stems inclination and lodging, reducing the effectiveness of water conveyance along the stem. Our study showed the need to include stemflow to better understand the hydrology of sugarcane plantations.

Plant invasion affects vegetation structure and sediment nitrogen stocks in subtropical mangroves.

Plant invasion can primarily affect the structure and functioning of terrestrial and aquatic ecosystems. Although there is evidence that plant invasion can modify organic matter dynamics in mangroves, it is uncertain whether and to which extent these changes can affect carbon (C) and nitrogen (N) dynamics in the sediment-plant system. Here, we measured: (i) the structure of native vegetation and C and N in the sediment-plant system in subtropical mangroves subjected to aquatic macrophytes invasion in southeastern Brazil. We answered the following questions: i) Do invaded mangroves differ in aboveground biomass compared to non-invaded mangroves?; ii) Are there C4 macrophytes in these sites? iii) What are the C and N stocks in sediment of invaded mangroves? We quantified C and N concentrations and the isotopic signature of such elements (δ13C and δ15N) in the sediment-plant system, the C and N stocks in the sediment (0-20 cm depth), and mangrove aboveground biomass. Mangrove aboveground biomass was lower at invaded compared to non-invaded sites reflecting the species displacement in invaded sites. The sediment at invaded mangroves did not significantly contribute to C4 sources because of the large predominance of both mangrove and invasive C3 plants. While sediment C stocks were similar among study sites (∼47 Mg ha-1), N stocks were lower at invaded (2.7 Mg ha-1) comparing to non-invaded (3.2 Mg ha-1) mangroves. The lower N stocks at invaded sites can reflect the higher leaf N concentrations and lower C:N ratios of invasive plants compared to mangroves. Thus, the effects of macrophytes invasion in subtropical mangroves are more apparent for vegetation structure and N stocks. C stocks alteration is expected the be detectable in the future.

Factors affecting the effectiveness of riparian buffers in retaining sediment: an isotopic approach.

Riparian forest width is a major driver of their capacity to retain sediments from agricultural fields. However, the relationship between forest width and ecosystem service provisioning may vary with local environmental conditions such as relief, soil, and vegetation types. In order to assess the effect of forest width, slope, hydraulic conductivity, and land cover (watershed scale) on the effectiveness of riparian buffers in retaining sediment from pastures cultivated with African C4 grasses, we used the natural abundance of carbon stable isotopes (δ13C) in the soil and stream organic sediments as indicators. The study was conducted in small streams of the upper Corumbá River basin, state of Goiás (Cerrado biome), Brazil. We found that slight increases from 2 to 5% mean slope were sufficient to change SOM to a mixture of C3 and C4 carbon sources inside the riparian forests. Therefore, hillslope's steepness and magnitude control soil transport downslope, but after reaching the riparian forest, sediment retention is strongly affected by the forest width. We also found that soil erosion leads to fine sediment deposition in agricultural streams, especially in those watersheds with a high occurrence of degraded pastures. We conclude that sites along the stream course with a combination of steep slopes, narrow forests, and intensive land use are the most vulnerable to sediment inputs and should be the focus of preservation and restoration by landscape managers.

Past and present land use influences on tropical riparian zones: an isotopic assessment with implications for riparian forest width determination / Influências pretéritas e presentes do uso da terra sobre zonas ripárias tropicais: uma avaliação isotópica com implicações para a determinação da largura de florestas ripárias

Abstract In this article, by using carbon stable isotopes, we assessed the past and present land use influences that riparian areas are subject within agricultural landscapes. Emphasis is given to the understanding of the effects of the 2012 Brazilian Forest Act on such areas. We selected five riparian areas within a highly C4 dominated agricultural landscape. Three of them had 30 meters native riparian forest buffer (NRFB) and two of them had 8 meter and no NRFB. We used three 100 meter-transects located 5, 15 and 30 meters relative to stream channel to obtain soil samples (0 - 10 cm). All riparian areas presented soil carbon isotopic signatures that are not C3 (native forests) irrespective of having or not 30 meters NRFB. Two cases presenting less than 30 meters NRFB had higher C4 derived carbon contribution. All of the other three areas that followed the 30 meters NRFB presented, to some degree, C4 derived carbon, which was attributed to C4 organic matter deposition originated from cultivated areas and, in one case, to the persistence of former exotic grasses. With the 2012 Forest Act allowing narrower buffers (< 30 meters), we expect C4 contributions to soil organic matter to remain high in riparian areas and streams within agricultural landscapes dominated by C4 plants where 30 meter NRFB is no longer required. Such contributions will likely continue to have detrimental effects on stream water quality and biota.

Resumo Neste artigo, ao utilizar isótopos estáveis de carbono, nós avaliamos as influências presentes e pretéritas do uso da terra a que as áreas ripárias estão sujeitas quando situadas dentro de paisagens agrícolas. Ênfase é dada ao entendimento dos efeitos do Código Florestal de 2012 em tais áreas. Nós selecionamos cinco áreas ripárias em uma paisagem agrícola altamente dominada por plantas C4. Três delas apresentam faixa ripária de floresta nativa (FRFN) de 30 metros de largura e as outras duas apresentam FRFN de 8 e 0 m (i.e. sem FRFN). Nós utilizamos três transectos de 100 metros localizados a 5, 15 e 30 metros de distância do canal fluvial para obter amostras de solo (0 - 10 cm). Todas as áreas ripárias apresentaram assinaturas isotópicas do carbono do solo que não são C3 (floresta nativa) independentemente de apresentarem ou não FRFN de 30 metros. Os dois casos em que FRFN era menor que 30 m apresentaram maior contribuição de carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4. Todas as outras três áreas com FRFN de 30 m também apresentaram, em algum grau, carbono oriundo de plantas C4 que foi atribuído è deposição de matéria orgânica de plantas C4 originada das áreas cultivadas e, em um caso, è persistência de gramíneas exóticas pré-existentes. Com o Código Florestal de 2012 permitindo FRFN mais estreitas (< 30 metros), nós esperamos que a contribuição de plantas C4 para a matéria orgânica permaneça alta em áreas ripárias e rios dentro de paisagens agrícolas dominadas por plantas C4 onde a FRFN de 30 m não é mais uma obrigação. Tais contribuições irão, provavelmente, continuar a ter efeitos prejudiciais è qualidade de água dos rios e à sua biota.

Water type and irrigation time effects on microbial metabolism of a soil cultivated with Bermuda-grass Tifton 85

This study investigated the microbial metabolism in Bermuda-grass Tifton 85 areas after potable-water and effluent irrigation treatments. The experiment was carried out in Lins/SP with samples taken in the rainy and dry seasons (2006) after one year and three years of irrigation management, and set up on an entirely randomized block design with four treatments: C (control, without irrigation or fertilization), PW (potable water + 520 kg of N ha-1 year-1); TE3 and TE0 (treated effluent + 520 kg of N ha-1 year-1) for three years and one year, respectively. The parameters determined were: microbial biomass carbon, microbial activity, and metabolic quotient. Irrigation with wastewater after three years indicated no alteration in soil quality for C and ET3; for PW, a negative impact on soil quality (microbial biomass decrease) suggested that water-potable irrigation in Lins is not an adequate option. Microbial activity alterations observed in TE0 characterize a priming effect.